Carbonylation



United States Patent 3,507,891 CARBONYLATION George W. Hearne, Lafayette, Kenneth E. Furman, Richmond, Rupert C. Morris, Berkeley, and John L. Van Winkle, San Lorenzo, Calif assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Sept. 6, 1966, Ser. No. 577,534 Int. Cl. Cllc 3/00 US. Cl. 260-4109 8 Claims ABSTRACT OF THE DISCLOSURE An improved process for the alkoxycarbonylation of nonacetylenic olefinically unsaturated aliphatic hydrocarbons with carbon monoxide and lower aliphatic alcohol carried out in the presence of, as catalyst, a complex of cobalt, carbon monoxide, and substituted pyridine without ortho substitution but with one or more hydrocarbon moiety substituents of at least one carbon on any ring C-atom produces lower alkyl esters of carboxylic acids high in normal content at high conversions and at relatively low temperatures and pressures.

This invention relates to an improved method of preparing lower alkyl esters of aliphatic carboxylic acids by the carbonylation of nonacetylenic olefinically unsaturated aliphatic hydrocarbon using a modified cobalt carbonylation catalyst in the presence of aliphatic alcohol, particularly lower aliphatic alcohol.

PRIOR ART It is known that esters and other functional derivatives of carboxylic acids such as amides and anhydrides may be prepared by reacting an olefin and carbon monoxide with an appropriate compound containing a replaceable hydrogen atom, e.g., water, alcohol, amines and acids, in the presence of a suitable carbonylation catalyst.

W. Reppe, US. Patent 2,689,261, describes the production of carboxylic acid esters by carbonylation, employing as catalysts complex metal-ammonium or -amine salts of metal carbonyl hydrides, for example to cobalto hexammine salts of cobalt carbonyl hydride or a pyridine-iron complex salt of cobalt carbonyl hydride. A. Matsuda and H. Uchida, Bull. Chem. Soc. Japan 38, 710 (1965), described the production of methyl butyrate by reacting propylene with carbon monoxide and methanol in the presence of dicobalt octacarbonyl and pyridine or other organic bases, and a small amount of hydrogen.

Heretofore, carbonylation processing has required high temperatures and pressures to carry out the reaction, thereby necessitating rather expensive and elaborate equipment. In general, temperatures in the range of 160-300 C. and pressures in the range of 15005000 p.s.i.g. are required.

Carbonylation catalysts usually employed have proven successful to a certain extent in the preparation of esters from lower a-olefins, carbon monoxide and a lower alcohol. However, when the olefin used is a higher olefin or an internal rather than an ot-olefin, conversion of reactants has been relatively low.

Certain difficulties have been found in the production of esters by reacting a-olefins with carbon monoxide and a lower alcohol in the presence of a cobalt carbonylpyridine catalyst. In such alkoxycarbonylation, the reactor efliuent contains substantial amounts of low-boiling materials, mainly excess lower alcohol, which must be removed before the desired ester can be overheated. After the removal of the low-boiling materials, the ester product may be recovered, for example by flashing. Cobalt carbonyl-pyridine catalyst is much less stable when not under carbon monoxide pressure and has been found to decompose, depositing cobalt metal under the conditions of ester-product flashing.

OBJECTS OF INVENTION It is an object of the present invention to provide an improved process for the alkoxycarbonylation of nonacetylenic olefinically unsaturated aliphatic hydrocarbons to esters whereby high conversions and high ester selectivities are obtained at relatively low temperatures and pressures.

It is also an object of the present invention to provide an improved process for the preparation of esters from higher nonacetylenic olefinically unsaturated aliphatic hydrocarbons and from nonacetylenic internal olefinically unsaturated aliphatic hydrocarbons by catalytic alkoxycarbonylation of these unsaturated hydrocarbons with carbon monoxide and alcohol.

It is a further object of this invention, to provide alkoxycarbonylation catalysts of improved heat stability.

THE INVENTION It has now been discovered that nonacetylenic olefinically unsaturated aliphatic hydrocarbons can be efficiently alkoxycarbonylated with carbon monoxide and lower aliphatic alcohol to form lower alkyl esters of carboxylic acids high in normal content at high conversions and under relatively mild reaction conditions when the reaction is carried out in the presence of, as catalyst, a complex of cobalt, carbon monoxide, and certain substituted pyridines without ortho substitution but with one or more hydrocarbon moiety substituents of at least one carbon on any ring C-atom. The ester then formed can be hydrolyzed to form carboxylic acid corresponding to the acyl portion of the ester.

REACTANTS The substituted pyridines which are useful for the complexes of this invention include a wide variety of pyridines not substituted in the ortho position, i.e., not substituted on a ring C-atom adjacent to the ring N-atom. Representative substituted pyridines are 3-methylpyridine, 4-methylpyridine, 4-butylpyridine, 3,4-dimethylpyridine, 3,5-dimethylpyridine, 4-ethylpyridine, 4-ethyl-3- methylpyridine, 3-ethyl-4-methylpyridine, 4-ethyl-3,5-dimethylpyridine, 4-(diphenylmethyl)pyridine, 4,4'-trimethylenedipyridine, isoquinoline, and the like. Isoquinoline can be considered a pyridine substituted in both the 3- and 4-positions each with a Z-carbon moiety (joined to form a benzo moiety). Similarly, 4,4'-trimethylenedipyridine can be considered as two pyridines each substituted in the 4-position with a l /z-carbon moiety. In the nonortho positions, hydrocarbon substitution is preferred to consist of a total of from one to 30 carbons. A particularly preferred class of hydrocarbon substituents are the lower alkyls of l to 4 carbons. In certain processing where less volatile substituted pyridine may be desired, another preferred class of substituents are hydrocarbyls of 10 to 20 carbons.

The nonacetylenic olefinically unsaturated aliphatic hydrocarbon to be alkoxycarbonylated is not particularly critical. A preferred group of nonacetylenic olefinically unsaturated aliphatic hydrocarbons includes aliphatic olefins, essentially monoolefins. A convenient group of starting materials is the aliphatic olefins in the range of C to C carbon atoms. One of the distinct advantages of the present invention is that it is applicable to internally located olefinic unsaturation as well as terminally located unsaturation. Internal olefins are isomerized during the process of the present invention to give conversion comparable to those obtained starting from aolefins.

The process of this invention is especially applicable in the alkoxycarbonylation of higher olefins since the esters so produced are substantially normal and can be hydrolyzed to the corresponding straight chain carboxylic acids useful in the formulation of soaps. For these reasons, olefins having from to 16 carbon atoms are pre ferred as starting materials. Cracked wax and cracked gas oil olefins, ethylene growth (Ziegler) olefins, and dehydrochlorinated mixed chlorinated n-parafiin olefins are all suitable.

Branched olefinic materials may also be used. Both internal and terminal (a) branched olefins react in the same manner as straight-chain olefins, producing esters having no greater degree of branching than the olefinic material reacted.

The alcohol used in the alkoxycarbonylation reaction is preferably a lower aliphatic alcohol and especially methanol, as the methyl esters thus formed are useful as solvents. Ethanol, propanol, isopropanol, and nbutanol are also useful. Ethylene glycol, propylene glycol, trimethylene glycol, and glycerol, as well as other lower alkane polyols are also useful. Lower alcohols are preferred also from the standpoint of subsequent hydrolysis to produce carboxylic acids, particularly those corresponding to higher olefins. The lower alcohols are more easily removed in the hydrolytic step. However, if desired, higher alcohols containing up to 22 carbon atoms can be used. In some instances, it is advantageous to use an alcohol having one more carbon atom than the olefin being alkoxycarbonylated. The ester thus formed contains the same number of carbon atoms in both the acid and alcohol moieties. For example, alkoxycarbonylation of l-eicosene using l-heneicosanol produces heneicosyl heneicosanoate.

REACTION CONDITIONS Prior art corbonylation reactions usually require temperatures in excess of 160 C., i.e. 160300 C., and pressures in excess of 1500 p.s.i.g. and usually in the range of 3000 to 5000 p.s.i.g. The process of the present invention carried out in the presence of, as catalyst, a complex of cobalt, carbon monoxide, and the hereinabove described substituted pyridine is operative at temperatures of between about 100 and about 200 C., preferably between about 120 and about 170 C., and even more preferably between about 140 and about 160 C., thereby resulting in a substantial heat reduction over prior art processes. Equally as significant is the reduction in pressure range from prior art processes. The present process requires pressures in the range of between about 200 to about 200 p.s.i.g. and is preferably operated at a pressure between about 600 and about 1400 p.s.i.g.

The pressure within the reaction zone is created primarily by carbon monoxide. However, if methanol is the lower alcohol used in the alkoxycarbonylation reaction, considerable pressure will be exerted by methanol vapors. As higher alcohols than methanol are used, less pressure due to the alcohol is present. The amount of carbon monoxide added to the process is dependent upon the pressures to be attained and is always in excess of the stoichiometric amount required to react with the olefin and for formation of the catalyst complex. Substantially pure carbon monoxide is used; however, if desired, a minor amount of hydrogen, not to exceed 10% of the added gas, may be employed as it further reduces alkoxycarbonylation reaction temperature and time.

The molar ratio of alcohol to unsaturated reactant in the alkoxycarbonylation reaction is usually between 06:1 and 10:1, with ratios between 08:1 and 6:1 being preferred.

The substituted pyridine-to-cobalt molar ratio is in substantial excess of unity, generally at least 2:1 and is preferably at least 4:1, and in some instances, between 6:1 and 18: 1. The cobalt concentration based on the total reaction charge is between 0.1 and 2% by weight and is preferably between 0.25 and 1.25% by weight. Concentrations of about 0.5 to 1.0% by weight, calculated as cobalt, are especially preferred.

The catalyst complex may be formed by introducing a preformed cobalt carbonyl such as dicobalt octacarbonyl into the reaction zone or by adding cobalt compounds, es pecially salts, e.g., cobalt alkanoates of 2 to 18 carbon atoms, convertible to cobalt carbonyl under carbonylation conditions, such as cobalt octanoate, to the reaction mixture.

If desired, the reaction may also be carried out in the presence of solvents, especially liquid aliphatic and aromatic hydrocarbons, e.g., decane, hexadecane, toluene, 1

xylenes, and tetralin.

The contact time in the alkoxycarbonylation zone may vary, depending upon reaction conditions, but is usually between 5 and 20 hours. The reaction may be carried out on a batch or continuous basis depending upon the size of the operation.

At the conclusion of the reaction, a stream of air may be passed through the product at room temperature or elevated temperature for 560 minutes to decompose the catalyst complex. This converts the cobalt into an oxidized state which is stable and will remain in solution during subsequent distillation of the reaction product. The soluble cobalt can be recycled to the alkoxycarbonylation step for the regeneration of catalyst- However, it is by far more prefereable not to decompose the catalyst complex but to recover it for recirculation and further usage. When the catalyst is a complex of cobalt, carbon monoxide, and pyridine, direct distillation of product containing the complex results in the formation of 10% or more metallic cobalt which cannot be readly reconverted to catalyst. When the catalyst is a complex of cobalt, carbon monoxide, and the substituted pyridines of the invention, for example 3,5-dimethylpyridine, the complex unexpectedly possesses high thermal stability enabling the removal of unreacted alcohol and unsaturated starting materialy by distillation followed by ester flashing and recycling of the stable active catalyst complex as bottoms thereform.

When a carboxylic acid or its alkali metal salt (e.g., soap) is the desired product, the crude ester product may be saponified and the product resulting therefrom further purified. For example, treatment with 20% aqueous potassium hydroxide while stirring and heating will hydrolyze the ester with concomitant distillation of the resulting lower alcohol, e.g., methanol. When evolution of alcohol is complete, the solution can be cooled and diluted with water, e.g., to give a 25% solution of potassium carboxylate. Although carbonyl impurities, such as acetals and aldehydes, are formed advantageously in lesser amounts when the catalyst is a complex of cobalt, carbon monoxide, and the substituted pyridines of the invention than when the catalyst is a complex of cobalt, carbon monoxide and pyridine, it is desirable that these impurities be removed. Their removal can be effected by extracting with solvents, e.g., methylene chloride, ether, benzene, and the like, or high-pressure, high-temperature steam distillation. Alternatively, the potassium carboxylate solution may be acidified with, for example, concentrated hydrochloric acid, and the carboxylic acid re covered by extraction or distillation. Carbonyl impurities can be removed from the carboxylic acids by treatment with aqueous sodium bisulfite.

The above saponification step is exemplary only. Any convenient hydrolysis step known in the art may be employed. For example, hydrolysis using inorganic acids may also be used. Hydrolysis methods useful in general are those mentioned by W. J. Hickinbottom, Reactions of Organic Compounds, 355-358, Longmans, Green and Co., London, 1957.

Alternatively, the ester product can be hydrogenated, employing any conventional hydrogenation step known 6 in the art, to form normal alcohol corresponding to the EXAMPLE III acyl portion of the ester as well as alcohol corresponding to th alk l moiety of the, t r, Six runs under the same conditions as used in Ex- EXAMPLE I ample I were carried out with 4-methylpyr1d1ne as ligand,

the exception being that different ligand-to-cobalt ratios A reaction zone previously purged with nitrogen was 5 were utilized. The results are summarized in Table 3.

TAB LE 3 Time required Normal Ligand/ Olefin for 50% Selectivity, percent by ester cobalt conversion, olefin Weight percent mole percent by conversion, by ratio weight hours Ester Acetal Aldehyde weight charged with a methanol/l-dodecene mixture in a molar It is evident that wide ranges in the ligand-to-cobalt ratio of 4:1. Pyridine or nonortho-substituted pyridine molar ratio can be employed within the scope of this ligand (see Table 1 below) and cobalt octanoate in a e0 process. molar ratio of 6:1 were added to give a cobalt concen- EXAMPLE IV tration of 1.0% by weight of the total reaction charge. The reaction zone was charged with carbon monoxide and maintained at 160 C. and a pressure of 1000 p.s.i.g.

Four runs under the same conditions as used in Example I were carried out with 4-methylpyridine as ligand, 25 the exception being that reaction zone temperature was CO f r an a e a fl period Of time, after Which the varied and maintained in each run at the value shown pressure was released and the product cooled and anin Table 4 concomitant with the results therefrom.

' TABLE 4 Time required Normal Olefin for 50% Selectivity, percent by ester conversion, olefin weight percent percent by conversion, by Weight hours Ester Acetal Aldehyde Weight Temperature, C.

93.3 3.2 99.1 0.0 0.2 30.1 98. 8 2. 7 98. 3 0. 9 0.3 80. 1 97.4 2.0 95.0 2.3 0 7 73.4 91.3 2.2 93.1 2.0 1 4 70.3 alyzed by gas-liquid chromatography (GLC). The results After removal of unreacted methanol and dodecene by are summarized in Table 1. distillation, a portion of the methyl tridecanoate was flash TABLE 1 Time Olefin required Normal conversion, for 50% Selectivity, percent by ester percent olefin Weight percent by conversion, by Ligand: weight hours Ester Acetal Aldehyde weight P ridine 99.1 2.2 93.7 2.7 2.0 75.0 3-methylpyr1d1ne 98. 9 2. 2 95. 9 1. 8 2. 78. 0 4-methylpyridine 99. 2 2. 7 93. 1 1. 0 0. 5 73. 3 i-ethylpyridiue. 98. 5 1. 7 97. 6 0. 9 1. 4 70. 5 3,4 dimethylpyiidine 93. 0 1. 7 99. 7 0. 3 0. 0 31. 5 3 5d1methylpyr1d1ne 98. 5 l. 7 97. 9 0.9 1. 3 80. 3 4-ethyl-3-methylpyi1d1ne 96. 7 2. 0 98. 4 0. 8 0. 8 81. 0 3-ethyl-4-methylpyridine. 95. 2 2. l 98. 2 1. 2 0. 7 81. 2 4-(dipheuylmethyl)pyridinea 98. 6 2. 2 95. 4 2. 6 2. l 77. 2 4,4-trimethylenedipyridine 04. 5 2. 8 97. 8 1. 0 1. 3 70. 0 Isoquinoline 98. 2 3. 4 96. 3 1. 7 1. 8 77. 0 4-ethyl-3,5-dimethylpyridine 87. 9 3. 4 99. 6 0. 4 0. 2 82. 1

(I) 1 CH3(CH2)"COCH3.

EXAMPLE II distilled, and the ester obtained was then heated at 85 90 C for about one hour with 207 a ueo ot s i m For purposes of comparison a number of ortho-substih 5 1 f a q us p a S u tuted pyridines were utilized as ligands following the di- 60 YdFOXl 6 H10 98 0 H1016 0f eslefloEvolved rections of Example I. The data, summarized in Table methanol removed f dlstlnatlon at 90 9 5 2 indicate that when these ligands are utilized the resulting light yellow solution was cooled and diluted with sults are inferior to those obtained either with the comdlstllled Water to give a Solutlon 0f Potasslum Saltsparative ligand pyridine or with the nonortho-substituted The aqueous Solutwn was then extracted several times pyridines of the invention. 65 with ISO-ml. portions of methylene chloride to remove TAB LE 2 Time required Normal Olefin for Selectivity, percent by ester 1 conversion, olefin weight percent percent by conversion, by Ligand weight hours Ester Acetol Aldehyde Weight Pyridine 99.1 2.2 93.7 2.7 2.0 75.0 86.3 6.5 67.3 22.4 8.6 44.4 74.3 0.4 07.3 22.7 7.5 43.0 00.8 7.9 71.2 20.4 0.7 45.0 14.1 34.0 0.0 0.0

1 CH (CH )"COCH carbonyl impurities. The aqueous solution, after extraction, was covered with a layer of 100 ml. of diethyl ether and concentrated HCl was added until the pH of the lower layer was 2. The layers were separated, the aqueous layer was washed with 100 ml. of ether, the combined organic We claim as our invention: 1. A process of preparing lower alkyl esters of carboxylic acids having a high normal content by the reaction of a nonacetylenic olefinically unsaturated aliphatic hy drocarbon with carbon monoxide and lower aliphatic phases were Washed of dlsmled.water.and alcohol in the presence of, as catalyst, a complex of the ether evaporated. Distillation of the remainder yieldcobalt, carbon monoxide, and a nonortho lower alkyled high quality tridecanoic acid.

substituted pyridine selected from the group consisting EXAMPLE V of 3,5-dimethylpyridine, 4,4'-trimethylenedipyridine, and The following runs summarized in Table 5 are typical 1O 4-et yl-3,5dimethylpyridine, at a temperature of from of the lower alcohols and olefins that can be used in about 100 to about 200 C. and at a pressure of from this process. The alcohol to olefin molar ratio used in about 200 to about 2000 p.s.i.g. Runs 25 was Runs 1 and 1 mole of Olefin 2. Aprocess according to claim lwherein the nonortho was for each of hydroxyl gr( )up lower alkyl-substituted pyridine is 3,5-dimethylpyridine. The ligand employed in Runs 2-5 was 3,5-d1methylpyr1- 3 A SS acco t l 1 h r th 1k 1 dine and in Runs 1 and 6, 4-methylpyridine. In all runs the proce l r mg 9 2 w e 6 y ligand-to-cobalt molar ratio was 6:1. The cobalt content pyndme'to'coba t mola? who Is kfetween F of the catalyst complexes was maintained at a value of A Process flccordmlg to 01mm Wh ere1n the by weight f cobalt based on h total reaction 20 acetylenic olefinically unsaturated aliphatic hydrocarbon charges. The reactions were carried out at 160 C. and i a straight-chain monoolefin and contains from 8 to 18 in the presence of sufficient carbon monoxide to maintain carbon atoms and the lower aliphatic alcohol contains a pressure of 1000 p.s.i.g. from 1 to 4 carbon atoms.

TABLE 5 Olefin conver- Selectivity, percent Normal Ester sion, by weight percent Percent by Time Aldeby Run Alcohol Olefin weight hours Ester Acetal hyde weight Composition 1 Methanol 1-dodecene- 96.2 1.6 97.3 0.0 1.8 80.5 CI'I3(CHQ)11CO2CH3 d0 99.1 1.9 96.7 1.6 0.9 80.0 CH3(CH2)11CO2CH2CH3 98.0 2.5 95.1 1.5 1.2 77.5 CH3(CH2)11CO2CH(CH3)2 100.0 2.9 95.5 1.0 1.1 80.2 CH3(CH2)11CO2CH2)2CH3 d 99.6 1.7 97.6 1.4 0.0 83.3 CH3(OH2)7CO2CH2(OH2)3 e 1,3propanediol(trido 99.5 2.6 {89.0 61.5 CH3(OH2)7CO2OH2CH2CH2OCO(CH2)7CH3 methylene glycol). 82 69.5 CH3(OH2)1COZCH2OH2OH2OH 1 Time required [or 50% olefin conversion.

EXAMPLE VI A reaction zone previously purged with nitrogen was charged with a methanol/dodecene mixture in a molar ratio of 4:1, one run utilizing l-dodecene and a like run utilizing internal dodecene. 3,5-dimethylpyridine ligand and cobalt octanoa'te in a molar ratio of 6:1 were added to give a cobalt concentration of 1.0% by weight of the total reaction charge. The reaction zone was charged with carbon monoxide and maintained at 160 C. and a pressure of 1000 p.s.i.g. CO for an ascertained period of time, after which the pressure was released and the product cooled and analyzed by gas-liquid chromatography 5. A process according to claim 4 wherein the straight chain monoolefin contains from 10 to 16 carbon atoms and the alcohol is methanol.

6. A process according to claim 5 wherein the reaction is carried out at from about to about C. and

at a pressure of from about 600 to about 1400 p.s.i.g.

7. A process according to claim 6 wherein the olefin is an a-olefin.

8. A process according to claim 6 wherein the olefin is an internal olefin.

The results show that this process is equally applicable to internal as well as OL-OlefiDS.

After removal of unreacted methanol and dodecene by distillation, the methyl tridecanoate was flash distilled, and a portion of this ester was placed in a pressure vessel in the presence of a copper chromite catalyst and hydrogenated at a maximum hydrogen pressure of 29 00 p.s.i.g. for about ten hours at 250 C. The resulting l-tridecanol and methanol obtained were separated by distillation.

References Cited Matsuda et al.: Bulletin of the Chem. Soc. Japan 38, pp. 710-715, May (196-5).

LORRAINE A. WEINBERGER, Primary Examiner R. S. WEISSBERG, Assistant Examiner US. Cl. X.R. 260-497 

